An Ankle Foot Orthotic (AFO) has been around for centuries and was created to substitute functionality of an ankle that had been lost to injury or disease. A common reason a person might be prescribed an AFO is a condition called foot-drop which is characterized by the inability to raise and/or lower the foot. Foot-drop can be caused nerve injury, neurological disorders, or muscular disorders. This incapacitation of the person's foot leads to unnatural gait and joint fatigue, as well as increasing the person's likelihood of tripping and becoming seriously injured. Hard plastic AFOs that hold a person's foot in a neutral position are the current standard for treating foot-drop. These AFOs can come in many different shapes and sizes which illustrate the wide variety in functionality of someone with foot-drop.
Unfortunately, the restrictive nature of the AFO can cause unnatural movements in the person's foot. These unnatural movements are more exaggerated when walking down stairs and ramps, as the natural thing to do is to land toe first, the opposite of what the AFO allows the person to do.
The most common existing manners of tracking human gait patterns and/or controlling active AFOs are stationary (clinic-based) optical or force-plate systems, inertial motion units (IMUs) that include accelerometers and/or gyroscopes, or force sensors that detect foot contact with the ground. External optical systems and force plates are strictly for in-clinic use, as they are static systems that cannot move with the user. IMUs can require significant additional signal processing to compensate for gyroscope drift or differentiation or integration of acceleration data. Those IMUs that also include magnetometers are susceptible to interference from external magnetic fields. Force sensors are limited to detecting ground contact and do not give other information specific to leg position or terrain/intensity level.
As far as gait tracking has been concerned, the general trend in gait tracking devices has been to increase the accuracy of the devices. Most modern gait tracking is achieved with the use of video systems that track markers attached to people. While increased accuracy is an important improvement, simpler, low-cost ways to measure the change in a person's gait over time are equally important.
Meanwhile, previously terrain detection has been purely a study for robotics. As a result, the techniques used for a non-robotic application have yet to be fully investigated. In the field of rehabilitation, orthotics, and prosthetics, terrain detection has been limited to characterizing the ground that the foot has already contacted, rather than predicting the ground that is approaching.